Coupled inductors with non-uniform winding terminal distributions

ABSTRACT

A coupled inductor includes a ladder magnetic core including two opposing rails extending in a lengthwise direction and joined by a plurality of rungs. The coupled inductor further includes a respective winding wound around each of the plurality of rungs. The plurality of rungs are divided into at least two groups of rungs, and a lengthwise separation distance between adjacent rungs in each group of rungs is less than a lengthwise separation distance between adjacent rungs of different groups of rungs.

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.15/018,318, filed Feb. 8, 2016, which is a divisional of U.S. patentapplication Ser. No. 13/802,363, filed Mar. 13, 2013. Each of theabove-mentioned applications is incorporated herein by reference.

BACKGROUND

It is known to electrically couple multiple switching sub-converters inparallel to increase switching power converter capacity and/or toimprove switching power converter performance. One type of switchingpower converter with multiple switching sub-converters is a“multi-phase” switching power converter, where the sub-converters, whichare often referred to as “phases,” switch out-of-phase with respect toeach other. Such out-of-phase switching results in ripple currentcancellation at the converter output filter and allows the multi-phaseconverter to have a better transient response than an otherwise similarsingle-phase converter.

As taught in U.S. Pat. No. 6,362,986 to Schultz et al., which isincorporated herein by reference, a multi-phase switching powerconverter's performance can be improved by magnetically coupling theenergy storage inductors of two or more phases. Such magnetic couplingresults in ripple current cancellation in the inductors and increasesripple switching frequency, thereby improving converter transientresponse, reducing input and output filtering requirements, and/orimproving converter efficiency, relative to an otherwise identicalconverter without magnetically coupled inductors.

Two or more magnetically coupled inductors are often collectivelyreferred to as a “coupled inductor” and have associated leakageinductance and magnetizing inductance values. Magnetizing inductance isassociated with magnetic coupling between windings; thus, the larger themagnetizing inductance, the stronger the magnetic coupling betweenwindings. Leakage inductance, on the other hand, is associated withenergy storage. Thus, the larger the leakage inductance, the more energystored in the inductor. Leakage inductance results from leakage magneticflux, which is magnetic flux generated by current flowing through onewinding of the inductor that is not coupled to the other windings of theinductor.

Integrated circuits including two or more power stages have beendeveloped for use in switching power converters. For example, FIG. 1shows a top plan view of a prior art four-phase buck switching powerconverter 100 including two integrated circuits 102 and a coupledinductor 104. In this document, specific instances of an item may bereferred to by use of a numeral in parentheses (e.g., integrated circuit102(1)) while numerals without parentheses refer to any such item (e.g.,integrated circuits 102). Coupled inductor 104 includes four windings106, and opposing ends of each winding form respective first and secondsolder tabs 108, 110. Solder tabs 108, 110 are uniformly distributedalong a length 112 of coupled inductor 104.

Each integrated circuit 102 includes two buck power stages (not shown)and two terminal sets 114. Each terminal set 114 include one or moreelectrical terminals, such as one or more solder balls, electricallycoupled to a common node and disposed on a bottom outer surface ofintegrated circuit 102. Terminal sets 114 are symbolically indicated bydashed line in the FIG. 1 top plan view because the terminal sets arenot visible when looking at the tops of integrated circuits 102. Eachterminal set 114 provides electrical interface to a respective powerstage of the integrated circuit. Both power stages and associatedterminal sets 114 are located in the same portion of the integratedcircuit, to ease integrated circuit design and construction. Thus,terminal sets 114 are located close together on integrated circuit 102.

Each terminal set 114 is electrically coupled to a respective firstsolder tab 108 by a conductor (not shown), such as a printed circuitboard (PCB) conductive “trace.” Each power stage and its respectivewinding 106 form part of a phase of buck switching converter 100.Accordingly, each integrated circuit 102 supports a respective pair ofconverter 100 phases, and coupled inductor 104 supports all four phasesof converter 100.

SUMMARY

In an embodiment, a coupled inductor includes a ladder magnetic corehaving a length, a width, and a height. The ladder magnetic coreincludes two rails extending in the lengthwise direction and joined inthe widthwise direction by at least first, second, third, and fourthrungs sequentially disposed along the length of the magnetic core. Thecoupled inductor further includes first, second, third, and fourthwindings wound at least partially around the first, second, third, andfourth rungs, respectively. The second rung is substantially closer inthe lengthwise direction to the first rung than to the third rung, andthe third rung is substantially closer in the lengthwise direction tothe fourth rung than to the second rung.

In an embodiment, a coupled inductor includes a ladder magnetic core, afirst winding, and a second winding. The ladder magnetic core has alength, a width, and a height. The ladder magnetic core includes firstand second rails extending in the lengthwise direction and joined in thewidthwise direction by at least first and second rungs. The firstwinding is wound, in a first orientation, at least partially around thefirst rung, and the second winding is wound, in a second orientation, atleast partially around the second rung. The second orientation isopposite to the first orientation. Opposing ends of the first windingform first and second solder tabs, respectively, and opposing ends ofthe second winding form third and fourth solder tabs, respectively. Thefirst and third solder tabs are disposed at least partially on a bottomouter surface of the first rail, and the second and fourth solder tabsare disposed at least partially on a bottom outer surface of the secondrail. The first and second windings are arranged such that currentflowing into the first and third solder tabs flows in a common directionaround each of the first and second rungs, respectively, when seenlooking cross-sectionally in the widthwise direction of the magneticcore.

In an embodiment, a coupled inductor includes a ladder magnetic core, afirst winding, a second winding, and a third winding. The laddermagnetic core has a length, a width, and a height. The ladder magneticcore includes two rails joined in the heightwise direction by at leastfirst, second, and third rungs respectively disposed along the length ofthe magnetic core. The first winding is wound, in a first orientation,at least partially around the first rung. The second winding is wound,in a second orientation opposite to the first orientation, at leastpartially around the second rung. The third winding is wound, in thefirst orientation, at least partially around the third rung. The secondrung is substantially closer in the lengthwise direction to the firstrung than to the third rung.

In an embodiment, a coupled inductor includes a ladder magnetic coreincluding two opposing rails extending in a lengthwise direction andjoined by a plurality of rungs. The coupled inductor further includes arespective winding wound around each of the plurality of rungs. Theplurality of rungs are divided into at least two groups of rungs, and alengthwise separation distance between adjacent rungs in each group ofrungs is less than a lengthwise separation distance between adjacentrungs of different groups of the at least two groups.

In an embodiment, a multi-phase switching power converter includes acoupled inductor including a ladder magnetic core having a length, awidth, and a height. The ladder magnetic core includes two railsextending in the lengthwise direction and joined in the widthwisedirection by at least first, second, third, and fourth rungssequentially disposed along the length of the magnetic core. The coupledinductor further includes first, second, third, and fourth windingswound at least partially around the first, second, third, and fourthrungs, respectively. The second rung is substantially closer in thelengthwise direction to the first rung than to the third rung, and thethird rung is substantially closer in the lengthwise direction to thefourth rung than to the second rung. The multi-phase switching powerconverter further includes first, second, third, and fourth switchingcircuits. Each switching circuit is adapted to repeatedly switch an endof a respective one of the first, second, third, and fourth windingsbetween at least two different voltage levels.

In an embodiment, a multi-phase switching power converter includes acoupled inductor including a ladder magnetic core, a first winding, anda second winding. The ladder magnetic core has a length, a width, and aheight. The ladder magnetic core includes first and second railsextending in the lengthwise direction and joined in the widthwisedirection by at least first and second rungs. The first winding iswound, in a first orientation, at least partially around the first rung,and the second winding is wound, in a second orientation, at leastpartially around the second rung. The second orientation is opposite tothe first orientation. Opposing ends of the first winding form first andsecond solder tabs, respectively, and opposing ends of the secondwinding form third and fourth solder tabs, respectively. The first andthird solder tabs are disposed at least partially on a bottom outersurface of the first rail, and the second and fourth solder tabs aredisposed at least partially on a bottom outer surface of the secondrail. The first and second windings are arranged such that currentflowing into the first and third solder tabs flows in a common directionaround each of the first and second rungs, respectively, when seenlooking cross-sectionally in the widthwise direction of the magneticcore. The multi-phase switching power converter further includes firstand second switching circuits. The first switching circuit is adapted torepeatedly switch the first solder tab between at least two differentvoltage levels, and the second switching circuit is adapted torepeatedly switch the third solder tab between at least two differentvoltage levels.

In an embodiment, a multi-phase switching power converter includes acoupled inductor, including a ladder magnetic core and first, second,and third windings. The ladder magnetic core has a length, a width, anda height. The ladder magnetic core includes two rails joined in theheightwise direction by at least first, second, and third rungsrespectively disposed along the length of the magnetic core. The firstwinding is wound, in a first orientation, at least partially around thefirst rung. The second winding is wound, in a second orientationopposite to the first orientation, at least partially around the secondrung. The third winding is wound, in the first orientation, at leastpartially around the third rung. The second rung is substantially closerin the lengthwise direction to the first rung than to the third rung.The multi-phase switching power converter further includes first,second, and third switching circuits. Each switching circuit is adaptedto repeatedly switch an end of a respective one of the first, second,and third windings between at least two different voltage levels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a top plan view of a prior art four-phase buck switchingpower converter including two integrated circuits and a coupledinductor.

FIG. 2 shows a perspective view of a coupled inductor having anon-uniform winding terminal distribution, according to an embodiment.

FIG. 3 shows a top plan view of the FIG. 2 coupled inductor.

FIG. 4 shows a cross-sectional view of the FIG. 2 coupled inductor.

FIG. 5 shows a top plan view of a magnetic core of the FIG. 2 coupledinductor.

FIG. 6 shows a perspective view of the FIG. 2 coupled inductor with arail of the magnetic core shown in outline form.

FIG. 7 shows a perspective view of a winding of the FIG. 2 coupledinductor.

FIG. 8 shows a perspective view of a winding of certain alternateembodiments of the FIG. 2 coupled inductor.

FIG. 9 shows a perspective view of another coupled inductor having anon-uniform winding terminal distribution, according to an embodiment.

FIG. 10 shows a top plan view of the FIG. 9 coupled inductor.

FIG. 11 shows a right side elevational view of the FIG. 9 coupledinductor.

FIG. 12 shows a bottom plan view of the FIG. 9 coupled inductor.

FIG. 13 shows a cross-sectional view of the FIG. 9 coupled inductor.

FIG. 14 shows a perspective view of the FIG. 9 coupled inductor with afirst rail and a leakage element of the inductor's magnetic core shownin outline form.

FIG. 15 shows a perspective view of a winding of the FIG. 9 coupledinductor at zero degree orientation, and FIG. 16 shows a perspectiveview of a winding of the FIG. 9 coupled inductor at 180 degreeorientation.

FIG. 17 shows one possible PCB footprint for use with the FIG. 9 coupledinductor, according to an embodiment.

FIG. 18 shows one possible PCB footprint for use with the coupledinductor of the switching power converter of FIG. 1.

FIG. 19 shows a perspective of view of an alternative winding at zerodegree orientation, and FIG. 20 shows a perspective view of thealternative winding at 180 degree orientation.

FIG. 21 shows one possible PCB footprint for use with the FIG. 9 coupledinductor and the windings of FIGS. 19 and 20, according to anembodiment.

FIG. 22 shows a perspective of a winding used in certain other alternateembodiments of the FIG. 9 coupled inductor.

FIG. 23 shows a cross-sectional view of a winding wound around a rung,to illustrate optimization of rung and winding geometry for minimumdirect current winding resistance.

FIG. 24 shows a perspective view of yet another coupled inductor havinga non-uniform winding terminal distribution, according to an embodiment.

FIG. 25 shows a front elevational view of the FIG. 24 coupled inductor.

FIG. 26 shows a bottom plan view of the FIG. 24 coupled inductor.

FIG. 27 shows a perspective view of the FIG. 24 coupled inductor with aportion of the magnetic core removed.

FIG. 28 shows an exploded perspective view of the magnetic core of theFIG. 24 coupled inductor.

FIG. 29 shows a front elevational view of the magnetic core of the FIG.24 coupled inductor.

FIG. 30 shows a perspective view of a winding of the FIG. 24 coupledinductor at zero degree orientation, and FIG. 31 shows a perspectiveview of a winding of the FIG. 24 coupled inductor at 180 degreeorientation.

FIG. 32 shows a top plan view of part of an eight-phase buck switchingpower converter including the coupled inductor of FIG. 2 electricallycoupled to four integrated circuits, according to an embodiment.

FIG. 33 is an electrical schematic of the FIG. 32 switching powerconverter.

FIG. 34 shows an idealized graph of normalized ripple current per phaseversus duty cycle, for different numbers of magnetically coupled phases,in a buck switching power converter of an arbitrary number of phases.

DETAILED DESCRIPTION OF THE EMBODIMENTS

While there are significant benefits to pairing coupled inductors withintegrated power stages, Applicant has discovered that there are alsodrawbacks. For example, consider again multi-phase switching powerconverter 100 of FIG. 1. A pitch 118 between integrated circuit terminalsets 114 is significantly smaller than a pitch 120 between solder tabs108. This pitch discrepancy makes it is impossible to align everyterminal set 114 with a respective solder tab 108. Misalignment ofterminal sets 114 and solder tabs 108 results in long length andassociated high impedance of some conductors between terminal sets 114and solder tabs 108. Additionally, converter 100 typically includesadditional components 124, such as resistors and capacitors, whichsupport integrated circuits 102. Additional components 124 may furtherimpede alignment of terminal sets 114 and solder tabs 108 byconstraining placement of integrated circuits 102 and associatedconductor routing.

Each terminal set 114 is separated from its respective solder tab by aseparation distance 122. Separation distances 122(1), 122(3) arerelatively short because terminal sets 114(1), 114(3) are aligned withsolder tabs 108(1), 108(3). In contrast, separation distances 122(2),122(4) are relatively long because terminal sets 114(2), 114(4) are notaligned with solder tabs 108(2), 108(4). Conductors spanning separationdistances 122(2), 122(4) will therefore be long and have relatively highimpedances.

High conductor impedance is undesirable, for example, because it causessignificant conduction losses at high current levels, thereby impairingconverter efficiency and causing undesired converter heating.Additionally, long conductors may cause electromagnetic interferencewith nearby circuitry, when high slew rate current flows through theconductors. Conductor impedance may be particularly significant when theconductors are PCB traces, because PCB traces are normally formed ofthin metallic foil having relatively high impedance, as compared torelatively thick metallic solder tabs 108 and associated windings 106.

Accordingly, Applicant has developed coupled inductors with non-uniformwinding terminal distributions, which facilitate aligning the windingterminals with integrated circuit terminals. As discussed below, use ofthese coupled inductors, instead of conventional coupled inductors, mayat least partially overcome one or more of the problems discussed above.

FIG. 2 shows a perspective view of a coupled inductor 200 having anon-uniform winding terminal distribution. Coupled inductor 200 includesa ladder magnetic core 202 and N windings 204. Although N is shown asbeing equal to eight, N could alternately be any integer greater thanthree. Magnetic core 202 has a length 206, a width 208, and a height210. FIG. 3 shows a top plan view of coupled inductor 200, with theoutlines of windings 204 shown by dashed lines where obscured by core202. FIG. 4 shows a cross-sectional view of coupled inductor 200 takenalong line A-A of FIG. 3, and FIG. 5 shows a top plan view of magneticcore 202. In this document, not all instances of every element arelabeled in the figures to promote illustrative clarity. For example,only some instances of windings 204 are labeled in FIG. 3.

Magnetic core 202 is formed of a magnetic material, such as a ferritematerial or a powdered iron material. Magnetic core 202 includes firstand second rails 212, 214 extending in the lengthwise 206 direction andseparated in the widthwise 208 direction. Magnetic core 210 furtherincludes N rungs 216, where each rung 216 joins first and second rails212, 214 in the widthwise 208 direction, as shown in FIG. 5. FIG. 6shows a perspective view of coupled inductor 200 with first rail 212shown in outline form, to show the interior of coupled inductor 200.Although rails 212, 214 and rungs 216 are shown as discrete magneticelements, two or more of these magnetic elements may be combined withoutdeparting from the scope hereof. Furthermore, in some embodiments,magnetic core 202 is a single-piece magnetic core that is formed, forexample, by molding magnetic material in a ladder shape.

Rungs 216 are divided into at least two separate groups 218, where eachgroup 218 includes two or more of the N rungs 216, as shown in FIG. 5.Adjacent rungs 216 within a common group 218 are separated by alengthwise separation distance 220. For instance, rungs 216(1) and216(2) of group 218(1) are separated by a separation distance 220(1),and rungs 216(3) and 216(4) of group 218(2) are separated by aseparation distance 220(2). Adjacent rungs 216 of different groups 218,in contrast, are separated by a lengthwise separation distance 222. Forinstance, rungs 216(2) and 216(3) are separated by a separation distance222(1), and rungs 216(4) and 216(5) are separated by a separationdistance 222(2). Each separation distance 220 is smaller than eachseparation distance 222, so that adjacent rungs within groups 218 aresubstantially closer together than adjacent rungs of different groups218. For example, rung 216(2) is substantially closer, in the lengthwise206 direction, to rung 216(1) than to rung 216(3). As another example,rung 216(3) is substantially closer, in the lengthwise direction, torung 216(4) than to rung 216(2).

Opposing ends of each winding 204 form respective solder tabs 224, 226,as shown, for example, in FIG. 3. Solder tabs 224, 226 serve asterminals for winding 204. Solder tabs 224, 226 are disposed at leastpartially on bottom outer surfaces 228, 230 of first and second rails212, 214, respectively. However, in some alternate embodiments, one ormore of solder tabs 224, 226 are replaced with a different terminaltype, such as a through-hole pin or a socket pin. FIG. 7 shows aperspective view of one winding 204 instance.

Each winding 204 is wound around a respective rung 216 such that currentflowing into each winding's first solder tab 224 flows around thewinding's respective rung 216 in a common direction, as seen whenlooking cross-sectionally in the widthwise 208 direction. For example,current flowing into each winding's first solder tab 224 flows aroundthe winding's respective rung 216 in a counterclockwise direction 232,as seen when looking cross-sectionally from first rail 212 towardssecond rail 214, as shown in FIG. 6. This winding configuration causescoupled inductor 200 to have inverse magnetic coupling, when either allfirst solder tabs 224 or all second solder tabs 226 are connected torespective switching nodes. Inverse magnetic coupling is required toachieve advantages associated with using coupled inductors, instead ofdiscrete inductors, in switching power converter applications.

Spaces 234 within ladder magnetic core 202, but outside of groups 218,provide leakage magnetic flux paths, thereby contributing to leakageinductance of windings 204 (see FIG. 3). For example, dashed line 236symbolically illustrates how space 234(1) provides a leakage magneticflux path for winding 204(2), although space 234(1) also providesleakage magnetic flux paths for other windings 204. The fact that spaces234 are within magnetic core 202 helps contain leakage magnetic fluxwithin coupled inductor 200, thereby helping minimize the likelihood ofelectromagnetic interference from leakage magnetic flux. Although notrequired, magnetic core 202 typically further includes N leakageelements or “teeth” 238, where each tooth 238 at least partially bridgesa widthwise 208 separation distance between first and second rails 212,214. Leakage teeth 238 and rung groups 218 are disposed in analternating manner along length 206, as shown in FIG. 5. Such leakagetooth 238 distribution helps achieve short paths for leakage fluxes frommultiple windings, which minimizes core losses.

Leakage teeth 238 decrease the leakage magnetic flux path reluctance inspaces 234, thereby promoting high and controllable leakage inductancevalues. Each leakage tooth 238 is typically separated from first rail212 by a gap 240. Gaps 240 help prevent magnetic saturation at highcurrent levels, and gap 240 dimensions can be adjusted during coupledinductor design to tune leakage inductance values. For example, leakageinductance can be increased by decreasing a thickness of gaps 240 in thewidthwise 208 direction. Additionally, winding 204 leakage inductancevalues can be adjusted during inductor 200 design by varying theconfiguration, such as the size and/or composition, of leakage teeth238.

In some alternate embodiments, such as where leakage teeth 238 areformed of a magnetic material with a distributed air gap, leakage teeth238 completely bridge the widthwise separation distance between firstand second rails 212, 214. Additionally, leakage teeth 238 couldalternately extend from first rail 212 toward second rail 214, such thatgaps 240 separate leakage teeth 238 from second rail 214. Furthermore,each leakage tooth 238 could be split into first and second sub-teeth(not shown) extending into space 234 from rails 212 and 214,respectively, such that a gap separates the sub-teeth in the widthwise208 direction.

The non-uniform rung 216 distribution along length 206 causes soldertabs 224, 226 to be non-uniformly distributed along length 206. Soldertabs 224 are divided into different groups 242 of two or more soldertabs 224, as shown in FIGS. 2 and 3. Lengthwise separation distances 244between adjacent solder tabs 224 within each group 242 are smaller thanlengthwise separation distances 246 between adjacent solder tabs 224 ofdifferent groups. For example, solder tab 224(2) is substantially closerin the lengthwise 206 direction to solder tabs 224(1) than to solder tab224(3), and solder tab 224(3) is substantially closer in the lengthwise206 direction to solder tab 224(4) than to solder tab 224(2). Suchnon-uniform solder tab distribution may facilitate aligning the soldertabs with an integrated circuit's terminals, such as discussed belowwith respect to FIG. 32.

The configuration of magnetic core 202 enables the majority of inductorvolume to be occupied by magnetic elements, namely rails 212, 214, rungs216, and leakage teeth 238, thereby promoting large magnetic corecross-sectional area per unit volume. Large magnetic corecross-sectional area promotes low core losses in magnetic core 202.

Although coupled inductor 200 is shown with two rungs 216 per rung group218, the number of rungs 216 per group 218 could be increased. Forexample, in certain alternate embodiments, N is equal to nine, and thenine rungs 216 are divided into three groups 218, where each groupincludes three rungs. Furthermore, although windings 204 are shown asbeing single-turn foil windings, windings 204 could be modified, as longas first solder tabs 224, or analogous terminals such as through-holepins, are non-uniformly distributed along length 206. For example, insome alternate embodiments, windings 204 are multi-turn windings, whichpromote large inductance values with small core losses. For example,FIG. 8 shows a perspective view of a two-turn wire winding 804, which isused in place of single-turn foil windings 204 in some alternateembodiments of coupled inductor 200. Opposing ends of winding 804 are,for example, coupled to terminals (not shown), such as solder tabs orthrough-hole pins. Moreover, some alternate embodiments include two ormore separate windings wound at least partially around each rung 216.The separate windings of each rung 216 are connected, for example, byexternal conductors, such as PCB traces, to form a multi-turn winding,such as using techniques similar to those taught in U.S. Pat. No.7,994,888 to Ikriannikov, which is incorporated by reference.

Multiple instances of coupled inductor 200 could be joined. For example,two instances of coupled inductor 200 could be joined in the lengthwise206 direction to form a coupled inductor including sixteen windings 204.

FIG. 9 shows a perspective view of another coupled inductor 900 having anon-uniform winding terminal distribution. Coupled inductor 900 includesa ladder magnetic core 902 and N windings 904. Although coupled inductor900 is shown with N being equal to eight, N could alternately be anyinteger greater than one without departing from the scope hereof.

Magnetic core 902 has a length 906, a width 908, and a height 910. FIG.10 shows a top plan view of coupled inductor 900, where the outlines ofwindings 904 are shown by dashed lines where obscured by magnetic core902. FIG. 11 shows a right side elevational view, FIG. 12 shows a bottomplan view, and FIG. 13 shows a cross-sectional view taken along line A-Aof FIG. 10.

Magnetic core 902 is formed of a magnetic material, such as a ferritematerial or a powdered iron material. Magnetic core 902 includes firstand second rails 912, 914 extending in the lengthwise 906 direction andjoined by N rungs 916, in a manner similar to magnetic core 202 ofcoupled inductor 200. Magnetic core 902 further includes a leakage tooth938 bridging a widthwise 908 separation distance between rails 912, 914.FIG. 14 shows a perspective view of coupled inductor 900 with first rail912 and leakage tooth 938 shown in outline form, to show the inductor'sinterior.

Leakage tooth 938 is disposed over rungs 916 in the heightwise 910direction, and a gap 940 typically separates leakage tooth 938 fromsecond rail 914. However, in some alternate embodiments, such as whereleakage tooth 938 is formed of a distributed air gap magnetic material,leakage tooth 938 completely bridges the widthwise separation distancebetween first and second rails 912, 914. Additionally, magnetic core 902could be modified such that leakage tooth 938 extends from second rail914 towards first rail 912, such that tooth 938 is separated from rail912 by gap 940. Furthermore, leakage tooth 938 could be split into firstand second sub-teeth (not shown) extending towards each other from rails912 and 914, respectively, such that a gap separates the sub-teeth inthe widthwise 908 direction. Moreover, although leakage tooth 938 isshown as extending along the entire length 906 to promote substantiallyequal leakage inductance values among windings 904, in some alternateembodiments, leakage tooth 938 only extends along part of length 906.Although rails 912, 914, rungs 916, and leakage tooth 938 are shown asbeing discrete magnetic elements, two or more of these magnetic elementsmay be combined without departing from the scope hereof. Furthermore, insome embodiments, magnetic core 908 is a single-piece magnetic core.

Leakage tooth 938 provides a leakage magnetic flux path and thereforecontributes to winding 904 leakage inductance. Leakage tooth 938 alsoelectrically shields the top of windings 904. Leakage inductance valuesof windings 904 can be adjusted during inductor 900 design by varyingthe configuration, such as the size and/or composition, of leakage tooth938, or by varying the widthwise 908 thickness of gap 940.

Opposing ends of each winding 904 form respective solder tabs 924, 926,which are structurally capable of surface mount soldering to a commonsubstrate, such as a PCB. See, for example, FIG. 10. Solder tabs 924,926 of each winding 904 serve as terminals for the winding, although insome alternate embodiments, one or more of solder tabs 924, 926 arereplaced with a different connector type, such as a through-hole pin ora socket pin. Solder tabs 924 are disposed on a bottom outer surface 928of first rail 912, and solder tabs 926 are disposed on a bottom outersurface 930 of second rail 914. Solders tab 924 and 926 of a givenwinding 904 are separated by a lengthwise separation distance 948.

Each winding 904 typically has a common geometric shape, as shown, topromote ease of winding procurement and manufacturing simplicity.However, windings 904 are wound around respective rungs 916 withalternating opposing orientations, such that windings 904(1), 904(3),904(5), and 904(7) have a zero degree orientation, while windings904(2), 904(4), 904(6), and 904(8) have a 180 degree orientation. Zerodegree orientation is characterized by solder tab 924 being disposed atleast partially on first rail bottom outer surface 928, and solder tab926 being disposed at least partially on second rail bottom outersurface 930. 180 degree orientation is characterized by solder tab 924being disposed at least partially on second rail bottom outer surface930, and solder tab 926 being disposed at least partially on first railbottom outer surface 928. Thus, windings 904 having a 180 degreeorientation are the mirror image of windings 904 having a zero degreeorientation, as seen when looking in the heightwise direction. FIG. 15shows a perspective view of a winding 904 instance at zero degreeorientation, and FIG. 16 shows a perspective view of a winding 904instance at 180 degree orientation, as seen when looking from first rail912 towards second rail 914.

Although windings 904 have alternating opposing orientations, thewindings are wound such that current flowing into each winding'sterminal at first rail 912 flows around the winding's respective rung916 in a common direction, as seen when looking cross-sectionally in thewidthwise 908 direction. For example, current flowing into solder tab924(1) of winding 904(1) flows in a counter-clockwise direction 932around rung 916(1), and current flowing into solder tab 926(2) ofwinding 904(2) flows in a counter-clockwise direction 932 around rung916(2), as seen when looking cross-sectionally from first rail 912towards second rail 914 (see FIG. 14). This winding configuration causescoupled inductor 900 to have inverse magnetic coupling, when allterminals along first rail 912 are electrically coupled to a respectiveswitching node.

Lengthwise separation distance 948 is typically minimized so that whenwindings 904 are wound around rungs 916 in alternating opposingorientations, solder tabs 924, 926 of adjacent windings are grouped inpairs along first rail bottom outer surface 928. For example, in someembodiments, separation distance 948 is fifty percent or less of a runglength 950 (see, e.g., FIGS. 14-16). The solder tabs 924, 926 on firstrail bottom outer surface 928 are divided into different groups 942,where each group includes two solder tabs, as shown in FIG. 10.Lengthwise separation distances 944 between adjacent solder tabs 924,926 within each group 942 are smaller than lengthwise separationdistances 946 between adjacent solder tabs of different groups. Suchnon-uniform solder tab distribution may facilitate aligning the soldertabs with an integrated circuit's terminals, such as discussed belowwith respect to FIG. 32. FIG. 17 shows a top plan view of one possiblePCB footprint 1700 for use with coupled inductor 900. As shown,separation distances 1752 between adjacent winding terminal pads withineach group 1754 of winding terminal pads are relatively small. Incontrast, FIG. 18 shows a top plan view of one possible PCB footprint1800 for use with coupled inductor 104 of FIG. 1. As can be seen,separation distances 1852 between adjacent winding terminals pads arerelatively large.

FIG. 19 shows a perspective view of a winding 1904. Winding 1904 issimilar to winding 904, but winding 1904 includes asymmetrical soldertabs 1924, 1926, such that solder tab 1926 is larger than solder tab1924. Windings 1904 are used in place of windings 904 in some alternateembodiments of coupled inductor 900. The asymmetrical solder tabs ofwinding 1904 helps maximize copper cross section area, while minimizingsolder tab separation, when windings 1904 are disposed in alternatingopposing orientations along length 906. Large solder tabs help tominimize conduction losses when the solder tabs supplement PCB traces.FIG. 19 shows winding 1904 at zero degree orientation, and FIG. 20 showswinding 1904 at 180 degree orientation, as seen when looking from firstrail 912 toward second rail 914. FIG. 21 shows a top plan view of onepossible PCB footprint 2100 for use with coupled inductor 900 includingwindings 1904 in place of windings 904. As shown, separation distances2152 between winding terminal pads are similar to separation distances1752 of the FIG. 17 footprint, even though a larger portion of the PCBsurface area is covered by solder tabs in the FIG. 21 footprint than inthe FIG. 17 footprint.

Although coupled inductor 900 is discussed above with respect tosingle-turn foil windings 904 or 1904, coupled inductor 900 couldalternately include multi-turn windings, which promote large inductancevalues with small core losses. For example, FIG. 22 shows a perspectiveview of a two-turn wire winding 2204, which is used in place ofsingle-turn foil windings 904, in some alternate embodiments of coupledinductor 900. Moreover, some alternate embodiments include two or moreseparate windings wound at least partially around each rung 916. Thewindings of each rung 916 are connected, for example, by externalconductors, such as PCB board traces, to form a multi-turn winding.

In both coupled inductors 200 and 900, the geometry of ladder magneticcore rungs 216, 916 and corresponding windings 204, 904 can be optimizedto minimize winding direct current (DC) resistance. FIG. 23, which showsa cross-sectional view of a winding 2304 wound around a rung 2316, helpsillustrate such optimization. Winding 2304 is analogous to windings 204,904, and rung 2316 is analogous to rungs 216, 916. DC resistance ofwinding 2304 is proportional to length (L) of winding 2304. Since L isaffected only by winding top 2356 and sides 2358, 2360, it can bedetermined that L is minimized when the ratio of rung length (l) andrung height (h) is two. Accordingly, minimum DC resistance occurs when:l/h=2   (EQN. 1)

Thus, in either coupled inductor 200 or 900, winding resistance isoptionally minimized by sizing the rungs and windings so that EQN. 1applies, although doing so may cause core length 206 to be relativelylong in inductor 200. EQN. 1, however, only holds when winding 2304 is asingle-turn winding. The optimal shape of rung cross-sectional area (A)becomes closer to a square as the number of turns of winding 2304 isincreased.

FIG. 24 shows a perspective view of another coupled inductor 2400 havinga non-uniform winding terminal distribution. Coupled inductor 2400includes a ladder magnetic core 2402 and N windings 2404. Althoughcoupled inductor 2400 is shown with N being equal to eight, N couldalternately be any integer greater than one. Magnetic core 2402 has alength 2406, a width 2408, and a height 2410. FIG. 25 shows a frontelevational view of coupled inductor 2400, FIG. 26 shows a bottom planview of the inductor, and FIG. 27 shows a perspective view of theinductor with a top rail 2412 of magnetic core 2402 removed.

FIG. 28 shows an exploded perspective view of magnetic core 2402, andFIG. 29 shows a side elevational view of magnetic core 2402. Magneticcore 2402 is formed of a magnetic material, such as a ferrite materialor a powdered iron material. Magnetic core 2408 includes first andsecond rails 2412, 2414 and N rungs 2416. Rails 2412, 2414 extend in thelengthwise 2406 direction and are joined by rungs 2416 in the heightwisedirection. First rail 2412 has opposing side outer surface 2462, 2464separated in the widthwise 2408 direction, and first rail 2412 hasopposing bottom and top outer surfaces 2428, 2430 separated in theheightwise 2410 direction. Rungs 2416 join first rail 2412 at top outersurface 2430. Although rails 2412, 2414 and rungs 2416 are shown asdiscrete magnetic elements, two or more of these magnetic elements maybe combined without departing from the scope hereof. Furthermore, insome embodiments, magnetic core 2402 is a single element magnetic core,such as a core formed by molding magnetic material in a ladder shape.

Rungs 2416 are divided into at least two separate groups 2418, whereeach group 2418 includes two or more of the N rungs 2416. Adjacent rungs2416 within a common group 2418 are separated by a lengthwise separationdistance 2420. For instance, rungs 2416(1) and 2416(2) of group 2418(1)are separated by a separation distance 2420(1), and rungs 2416(3) and2416(4) of group 2418(2) are separated by a separation distance 2420(2).Adjacent rungs 2416 of different groups 2418, in contrast, are separatedby a lengthwise separation distance 2422. For instance, rungs 2416(2)and 2416(3) are separated by a separation distance 2422(1), and rungs2416(4) and 2416(5) are separated by a separation distance 2422(2). Eachseparation distance 2420 is smaller than each separation distance 2422,so that adjacent rungs within groups 2418 are substantially closertogether than adjacent rungs of different groups 2418. For example, rung2416(2) is substantially closer, in the lengthwise 2406 direction, torung 2416(1) than to rung 2416(3). As another example, rung 2416(3) issubstantially closer, in the lengthwise direction, to rung 2416(4) thanto rung 2416(2).

Opposing ends of each winding 2404 form respective first and secondsolder tabs 2424, 2426, which are structurally capable of surface mountsoldering to a common substrate, such as a PCB. See, for example, FIG.26. Solder tabs 2424, 2426 of each winding 2404 serve as terminals forthe winding, although in some alternate embodiments, one or more ofsolder tabs 2424, 2426 are replaced with a different connector type,such as a through-hole pin or a socket pin. Solder tabs 2424, 2426 aredisposed on a bottom outer surface 2428 of first rail 2412.

Each winding 2404 typically has a common geometric shape, as shown, topromote ease of winding procurement and manufacturing simplicity.However, windings 2404 are wound around respective rungs 2416 withalternating opposing orientations, such that windings 2404(1), 2404(3),2404(5), and 2404(7) have a zero degree orientation, while windings2404(2), 2404(4), 2404(6), and 2404(8) have a 180 degree orientation.Zero degree orientation is characterized by winding 2404 wrapping aroundfirst side outer surface 2462 to reach bottom outer surface 2428. 180degree orientation is characterized by winding 2404 wrapping aroundsecond side outer surface 2464 to reach bottom outer surface 2428. Thus,windings 2404 having a 180 degree orientation are the mirror image ofwindings 2404 having a zero degree orientation, as seen when looking inthe heightwise direction. FIG. 30 shows a perspective view of a winding2404 instance at zero degree orientation, and FIG. 31 shows aperspective view of a winding 2404 instance at 180 degree orientation,as seen when looking at coupled inductor 2400 toward first side outersurface 2462.

Each winding 2404 is wound around a respective rung 2416 such thatcurrent flowing into each winding's first solder tab 2424 flows aroundthe winding's respective rung 2416 in a common direction, as seen whenlooking cross-sectionally in the heightwise 2410 direction. For example,current flowing into each winding's first solder tab 2424 flows aroundthe winding's respective rung 2416 in a counterclockwise direction 2432,as seen when looking cross-sectionally from second rail 2414 towardsfirst rail 2412, as shown in FIG. 27. This winding configuration causescoupled inductor 2400 to have inverse magnetic coupling, when each firstsolder tab 2424 is electrically coupled to a respective switching node.

Spaces 2434 within ladder magnetic core 2402, but outside of groups2418, provide leakage magnetic flux paths, thereby contributing toleakage inductance of windings 2404 (see FIG. 29). The fact that spaces2434 are within magnetic core 2402 helps contain leakage magnetic fluxwithin coupled inductor 2400, thereby helping minimize the likelihood ofelectromagnetic interference from leakage magnetic flux. Although notrequired, magnetic core 2402 typically further includes N leakageelements or “teeth” 2438, where each tooth 2438 is disposed on firstrail 2412 and at least partially bridges a heightwise 2410 separationdistance between first and second rails 2412, 2414. Leakage teeth 2438and rung groups 2418 are disposed in an alternating manner along length2406, as shown, for example, in FIGS. 28 and 29. Such leakage tooth 2438distribution helps achieve short paths for leakage fluxes from multiplewindings, which minimizes core losses.

Leakage teeth 2438 decrease the leakage magnetic flux path reluctance inspaces 2434, thereby promoting high and controllable leakage inductancevalues. Each leakage tooth 2438 is typically separated from second rail2412 by a gap 2440. Gaps 2440 help prevent magnetic saturation at highcurrent levels, and gap 2440 dimensions can be adjusted during coupledinductor design to tune leakage inductance values. For example, leakageinductance can be increased by decreasing a thickness of gaps 2440 inthe heightwise 2410 direction. Additionally, winding 2404 leakageinductance values can be adjusted during inductor 2400 design by varyingthe configuration, such as the size and/or composition, of leakage teeth2438.

In some alternate embodiments, such as where leakage teeth 2438 areformed of a magnetic material with a distributed air gap, leakage teeth2438 completely bridge the heightwise separation distance between firstand second rails 2412, 2414. Additionally, leakage teeth 2438 couldalternately extend from second rail 2412 toward first rail 2414, suchthat gaps 2440 separate leakage teeth 2438 from first rail 2412.Furthermore, each leakage tooth 2438 could be split into first andsecond sub-teeth (not shown) extending into space 2434 from rails 2412and 2414, respectively, such that the sub-teeth are separated by a gapin the widthwise 2408 direction.

The non-uniform rung 2416 distribution along length 2406 and thealternating winding 2404 orientation causes solder tabs 2424, 2426 to benon-uniformly distributed along length 2406. First solder tabs 2424 aredivided into different groups 2442 of two or more solder tabs 2424, asshown in FIG. 26. Lengthwise separation distances 2444 between adjacentfirst solder tabs 2424 within each group 2442 are smaller thanlengthwise separation distances 2446 between adjacent solder tabs 2424of different groups. For example, solder tab 2424(2) is substantiallycloser in the lengthwise 2406 direction to solder tabs 2424(1) than tosolder tab 2424(3), and solder tab 2424(3) is substantially closer inthe lengthwise 2406 direction to solder tab 2424(4) than to solder tab2424(2). Such non-uniform solder tab distribution may facilitatealigning the solder tabs with an integrated circuit's terminals, such asdiscussed below with respect to FIG. 32.

The configuration of magnetic core 2402 enables the majority of inductorvolume to be occupied by magnetic elements, namely rails 2412, 2414,rungs 2416, and leakage teeth 2438, thereby promoting large magneticcore cross-sectional area per unit volume. Large magnetic corecross-sectional area promotes low core losses in magnetic core 2402.

Although windings 2404 are shown as being single-turn foil windings,windings 2404 could be modified, as long as first solder tabs 2424, oranalogous terminals such as through-hole pins, are non-uniformlydistributed along length 2406. For example, in some alternateembodiments, windings 2404 are multi-turn windings, which promote largeinductance values with small core losses.

Multiple instances of coupled inductor 2400 could be joined. Forexample, two instances of coupled inductor 2400 could be joined in thelengthwise 2406 direction to form a coupled inductor including sixteenwindings 2404.

One possible application of coupled inductors 200, 900, and 2400 is inswitching power converters, including but not limited to multi-phasebuck converters, multi-phase boost converters, or multi-phase buck-boostconverters. For example, FIG. 32 shows a top plan view of part of aneight-phase buck switching power converter 3200 including an instance ofcoupled inductor 200. The outlines of windings 204 are denoted by dashedlines in FIG. 32 where obscured by magnetic core 202. FIG. 33 is anelectrical schematic of converter 3200. Converter 3200 includes fourintegrated circuits 3202, where each integrated circuit 3202 includestwo buck power stages or switching circuits 3204 (not visible in FIG.32) and two terminal sets 3206. Each terminal set 3206 include one ormore electrical terminals, such as one or more solder balls, disposed ona bottom outer surface of integrated circuit 3202. Terminal sets 3206are symbolically indicated by dashed line in the FIG. 32 top plan viewbecause the terminal sets are not visible when looking at the tops ofintegrated circuits 3202. Each terminal set 3206 provides electricalinterface to a switching node Vx of a respective switching circuit 3204.

Coupled inductor 200 and integrated circuits 3202 are disposed on a PCB3208, and solder tabs 224, 226 are soldered to the PCB. Each terminalset 3206 is electrically coupled to a respective first solder tab 224 bya PCB trace 3210. Each switching circuit 3204 and its respective winding204 form part of a respective phase 3212 of converter 3200. Accordingly,each integrated circuit 3202 supports a respective pair of phases 3212.For example, integrated circuit 3202(1) supports phases 3212(1),3212(2). Coupled inductor 200, however, supports all eight phases 3212of converter 3200, such that all eight phases are magnetically coupled.Only three of the eight phases 3212 are shown in the FIG. 33 schematicto promote illustrative clarity

Each switching circuit 3204 is electrically coupled to an input port3216, which is in turn electrically coupled to an electric power source3218. An output port 3220 is electrically coupled to an output node Vo,and each second solder tab 226 is electrically coupled to output nodeVo.

A controller 3222 causes each switching circuit 3204 to repeatedlyswitch its respective first solder tab 224 between electric power source3218 and ground, thereby switching its first solder tab between twodifferent voltage levels, to transfer power from electric power source3218 to a load (not shown) electrically coupled across output port 3220.Controller 3222 typically causes switching circuits 3204 to switch at arelatively high frequency, such as at 100 kilohertz or greater, topromote low ripple current magnitude and fast transient response, aswell as to ensure that switching induced noise is at a frequency abovethat perceivable by humans. Additionally, in certain embodiments,controller 3222 causes switching circuits 3204 to switch out-of-phasewith respect to each other to improve transient response and promoteripple current cancelation in output capacitors 3224. In someembodiments, controller 3222 is integrated in one or more integratedcircuits 3202. In other embodiments, controller 3222 is implemented bycircuitry (not shown) external to integrated circuits 3202.

Each switching circuit 3204 includes a control switching device 3226that alternately switches between its conductive and non-conductivestates under the command of controller 3222. Each switching circuit 3204further includes a freewheeling device 3228 adapted to provide a pathfor current through its respective winding 204 when the controlswitching device 3226 of the switching circuit transitions from itsconductive to non-conductive state. Freewheeling devices 3228 may bediodes, as shown, to promote system simplicity. However, in certainalternate embodiments, freewheeling devices 3228 may be supplemented byor replaced with a switching device operating under the command ofcontroller 3222 to improve converter performance. For example, diodes infreewheeling devices 3228 may be supplemented by switching devices toreduce freewheeling device 3228 forward voltage drop. In the context ofthis disclosure, a switching device includes, but is not limited to, abipolar junction transistor, a field effect transistor (e.g., aN-channel or P-channel metal oxide semiconductor field effecttransistor, a junction field effect transistor, a metal semiconductorfield effect transistor), an insulated gate bipolar junction transistor,a thyristor, or a silicon controlled rectifier.

Controller 3222 is optionally configured to control switching circuits3204 to regulate one or more parameters of converter 3200, such as inputvoltage, input current, input power, output voltage, output current, oroutput power. Converter 3200 typically includes one or more inputcapacitors 3230 electrically coupled across input port 3216 forproviding a ripple component of switching circuit 3204 input current.Additionally, one or more output capacitors 3224 are generallyelectrically coupled across output port 3220 to shunt ripple currentgenerated by switching circuits 3204. Input capacitors 3230, outputcapacitors 3224, electric power source 3218, input port 3216, and outputport 3220 are not shown in FIG. 32.

Converter 3200 could be modified to have a different number of phases3212. For example, converter 3200 could be modified to have only fourphases 3212 and use a four-winding embodiment of coupled inductor 200.Converter 3200 could also be modified to use one of the other coupledinductors disclosed herein, such as inductor 900 or 2400, in place ofinductor 200. Furthermore, converter 3200 could be modified toincorporate switching circuits formed of discrete components, instead ofswitching circuits 3204 integrated in integrated circuits 3202, at thecost of an increased parts count and a possible performance reduction.Moreover, converter 3200 could also be modified to have a differenttopology, such as a multi-phase boost or a multi-phase buck-boostconverter topology, or an isolated topology, such as a flyback orforward converter topology.

Use of coupled inductor 200, 900, or 2400, instead of a conventionalcoupled inductor, may offer one or more advantages in a multi-phaseswitching power converter application. For example, the non-uniformwinding terminal distribution of inductors 200, 900, and 2400 may enablethe winding terminals to be substantially aligned with terminals ofassociated integrated circuits, thereby helping minimize length ofconductors connecting the terminals and winding terminals. For example,consider again switching converter 3200 of FIG. 32. The non-uniformdistribution of first solder tabs 224 enables the first solder tabs tobe substantially aligned with integrated circuit terminal sets 3206,thereby enabling separation distances 3232 to be relatively short. Shortseparation distance 3232 helps minimize trace 3210 length and associatedimpedance, thereby helping minimize trace conduction losses andlikelihood of electromagnetic interference from traces 3210.Accordingly, use of coupled inductor 200, 900, or 2400, instead of aconventional coupled inductor, in an integrated power stage applicationmay improve converter efficiency, reduce converter heating, and promoteelectromagnetic compatibility with nearby circuitry.

As another example, use of coupled inductor 200, 900, or 2400, insteadof a conventional coupled inductor, may enable an increase in the numberof magnetically coupled phases without a significant increase inconverter volume. Specifically, the non-uniform winding terminaldistributions of inductors 200, 900, and 2400 allow windings to beplaced close together, while achieving a “pin out” that allows for shortconnections to associated switching circuits. For instance, as discussedabove with respect to FIG. 32, the coupled inductor 200 solder tabdistribution allows for short connections to integrated circuit terminalsets 3206. Accordingly, the non-uniform winding terminal distributionsof coupled inductors 200, 900, and 2400 helps enable close spacing ofwindings, thereby often allowing coupled inductors 200, 900, and 2400 toinclude more windings than conventional coupled inductors of similarsize. Indeed, although coupled inductor 200 in converter 3200 hasroughly the same outer dimensions as conventional coupled inductor 104of prior art converter 100 (FIG. 1), coupled inductor 200 has twice thenumber of windings as coupled inductor 104. Thus, converter 3200 hastwice the number of phases as prior art converter 100, even though bothconverters occupy approximately the same volume of space.

The magnetic coupling of a large number switching power converterphases, which is potentially enabled by use of coupled inductor 200,900, or 2400 instead of a conventional coupled inductor, may offersignificant benefits. Applicant has discovered that increasing thenumber of magnetically coupled phases in a switching power converter cansignificantly lower per-phase switching current magnitude, even ifper-phase energy storage inductance remains unchanged. For example, FIG.34 shows an idealized graph of normalized ripple current per phaseversus duty cycle, for different numbers of magnetically coupled phases,in a buck switching power converter. As can be appreciated from FIG. 34,increasing the number of magnetically coupled phases, significantlydecreases ripple current magnitude even if inductance value in eachphase remains the same. Decreasing ripple current magnitude reducesconduction losses and also reduces output voltage ripple. In comparison,merely increasing the number of phases, without magnetic coupling thephases, typically requires a proportional increase in the inductancevalue per phase, because current per phase will decrease in proportionto the number of phases, and ripple current per phase must thereforeproportionally decrease to maintain efficiency.

Furthermore, increasing the number of magnetically coupled phasesreduces effective total inductance, assuming leakage inductance perphase remains unchanged as the number of magnetically coupled phasesincreases. A decrease in effective total inductance, in turn, allows fora faster rate of change of switching power converter current. Thus,increasing the number of magnetically coupled phases in a switchingpower converter may improve converter transient response.

Moreover, an increase in number of switching power converter phasesnormally decreases magnitude of current per phase. Such decrease incurrent magnitude may enable use of higher resistance inductor windings,thereby potentially allowing use of multi-turn windings. Use ofmulti-turn windings, in turn, helps reduce magnetic core losses byreducing required magnetic core flux density at a given inductancelevel.

Combinations of Features

Features described above as well as those claimed below may be combinedin various ways without departing from the scope hereof. The followingexamples illustrate some possible combinations:

(A1) A coupled inductor may include a ladder magnetic core having alength, a width, and a height. The ladder magnetic core may include tworails extending in the lengthwise direction and joined in the widthwisedirection by at least first, second, third, and fourth rungssequentially disposed along the length of the magnetic core. The coupledinductor may further include first, second, third, and fourth windingswound at least partially around the first, second, third, and fourthrungs, respectively. The second rung may be substantially closer in thelengthwise direction to the first rung than to the third rung. The thirdrung may be substantially closer in the lengthwise direction to thefourth rung than to the second rung.

(A2) In the coupled inductor denoted as (A1), the ladder magnetic coremay further include a first leakage tooth at least partially bridging awidthwise separation distance between the two rails, where the firstleakage tooth is disposed along the length of the ladder magnetic corebetween the second and third rungs.

(A3) In the coupled inductor denoted as (A2), the first leakage toothmay bridge less than all of the widthwise separation distance betweenthe two rails.

(A4) In either of the coupled inductors denoted as (A2) or (A3), theladder magnetic core may further include a second leakage tooth at leastpartially bridging the widthwise separation distance between the tworails, and the third and fourth rungs may be disposed along the lengthof the ladder magnetic core between the first and second leakage teeth.

(A5) In any of the coupled inductors denoted as (A1) through (A4),respective ends of the first, second, third, and fourth windings mayform first, second, third, and fourth solder tabs, respectively, wherethe first, second, third, and fourth solder tabs are structurallycapable of surface mount soldering to a common substrate. The secondsolder tab may be substantially closer in the lengthwise direction tothe first solder tab than to the third solder tab. The third solder tabmay be substantially closer in the lengthwise direction to the fourthsolder tab than to the second solder tab.

(A6) In the coupled inductor denoted as (A5), the two rails may includefirst and second rails, and each of the first, second, third, and fourthsolder tabs may be at least partially disposed on a bottom outer surfaceof the first rail.

(A7) In either of the coupled inductors denoted as (A5) or (A6), thewindings may be arranged such that current flowing into the first,second, third, and fourth solder tabs flows in a common direction aroundeach of the first, second, third, and fourth rungs, respectively, whenseen looking cross-sectionally in the widthwise direction of themagnetic core.

(A8) In any of the coupled inductors denoted as (A1) through (A7), thefirst, second, third, and fourth windings may have respective leakageinductance values that are substantially identical.

(B1) A coupled inductor may include a ladder magnetic core having alength, a width, and a height. The ladder magnetic core may includefirst and second rails extending in the lengthwise direction and joinedin the widthwise direction by at least first and second rungs. Thecoupled inductor may further include first and second windings. Thefirst winding may be wound, in a first orientation, at least partiallyaround the first rung. The second winding may be wound, in a secondorientation, at least partially around the second rung, where the secondorientation is opposite to the first orientation. Opposing ends of thefirst winding may form first and second solder tabs, respectively, andopposing ends of the second winding may form third and fourth soldertabs, respectively. The first and third solder tabs may be disposed atleast partially on a bottom outer surface of the first rail, and thesecond and fourth solder tabs may be disposed at least partially on abottom outer surface of the second rail. The first and second windingsmay be arranged such that current flowing into the first and thirdsolder tabs flows in a common direction around each of the first andsecond rungs, respectively, when seen looking cross-sectionally in thewidthwise direction of the magnetic core.

(B2) In the coupled inductor denoted as (B1), each of the first andsecond windings may have a common geometric shape.

(B3) In either of the coupled inductors denoted as (B1) or (B2), theladder magnetic core may further include a third rung joining the firstand second rails in the widthwise direction, and the coupled inductormay further include a third winding wound, in the first orientation, atleast partially around the third rung.

(B4) In the coupled inductor denoted as (B3): (i) opposing ends of thethird winding may form fifth and sixth solder tabs, respectively, (ii)the fifth solder tab may be disposed at least partially on the bottomouter surface of the first rail, (iii) the sixth solder tab may bedisposed at least partially on the bottom outer surface of the secondrail, and (iv) the windings may be arranged such that current flowinginto the first, third, and fifth solder tabs flows in a common directionaround each of the first, second, and third rungs, respectively, whenseen looking cross-sectionally in the widthwise direction of themagnetic core.

(B5) In the coupled inductor denoted as (B4): (i) the third solder tabmay be disposed, in the lengthwise direction between the first and fifthsolder tabs, (ii) the fourth solder tab may be disposed, in thelengthwise direction, between the second and sixth solder tabs, and(iii) each of the second, third, and sixth solder tabs may be largerthan each of the first, fourth, and fifth solder tabs.

(B6) In any of the coupled inductors denoted as (B1) through (B5), theladder magnetic core may further include a leakage tooth extendingbetween the first and second rails in the widthwise direction, where theleakage tooth is disposed, in the heightwise direction, over at leastone of the first, second, and third rungs.

(B7) In any of the coupled inductors denoted as (B1) through (B6), thefirst, second, and third windings may have respective leakage inductancevalues that are substantially identical.

(B8) In any of the coupled inductors denoted as (B1) through (B7), eachof the first and second windings may be a single-turn winding, each ofthe first and second rungs may have a cross section in the lengthwiseand heightwise directions, and a rung length by a rung height may besubstantially equal to two.

(C1) A coupled inductor may include a ladder magnetic core having alength, a width, and a height. The ladder magnetic core may include tworails joined in the heightwise direction by at least first, second, andthird rungs respectively disposed along the length of the magnetic core.The coupled inductor may further include first, second, and thirdwindings. The first winding may be wound, in a first orientation, atleast partially around the first rung, and the second winding may bewound, in a second orientation opposite to the first orientation, atleast partially around the second rung. The third winding may be wound,in the first orientation, at least partially around the third rung. Thesecond rung may be substantially closer in the lengthwise direction tothe first rung than to the third rung.

(C2) In the coupled inductor denoted as (C1), each of the first, second,and third windings may have a common geometrical shape.

(C3) In either of the coupled inductors denoted as (C1) or (C2): (i)respective ends of the first, second, and third windings may form first,second, and third solder tabs, respectively, (ii) the first, second, andthird solder tabs may be structurally capable of surface mount solderingto a common substrate, and (iii) the second solder tab may besubstantially closer in the lengthwise direction to the first solder tabthan to the third solder tab.

(C4) In the coupled inductor denoted as (C3), each of the first, second,and third solder tabs may be at least partially disposed on a bottomouter surface of a common one of the two rails.

(C5) In any of the coupled inductors denoted as (C1) through (C4): (i)the ladder magnetic core may further include a fourth rung joining thefirst and second rails in the heightwise direction, (ii) the third rungmay be disposed, in the lengthwise direction, between the first leakagetooth and the fourth rung, (iii) the third rung may be substantiallycloser in the lengthwise direction to the fourth rung than to the secondrung, and (iv) the coupled inductor further may include a fourth windingwound, in the second orientation, at least partially around the fourthrung.

(C6) In the coupled inductor denoted as (C5): (i) the ladder magneticcore may further include first and second leakage teeth at leastpartially bridging a heightwise separation distance between the tworails, (ii) the first leakage tooth may be disposed on at least one ofthe two rails between the second and third rungs, and (iii) the thirdand fourth rungs may be disposed along the length of the ladder magneticcore between the first and second leakage teeth.

(C7) In any of the coupled inductors denoted as (C1) through (C5), theladder magnetic core may further include a first leakage tooth at leastpartially bridging a heightwise separation distance between the tworails, where the first leakage tooth is disposed on at least one of thetwo rails between the second and third rungs.

(C8) In any of the coupled inductors denoted as (C1) through (C7), thefirst, second, third, and fourth windings may have respective leakageinductance values that are substantially identical.

(D1) A multi-phase switching power converter may include a coupledinductor including a ladder magnetic core having a length, a width, anda height. The ladder magnetic core may include two rails extending inthe lengthwise direction and joined in the widthwise direction by atleast first, second, third, and fourth rungs sequentially disposed alongthe length of the magnetic core. The coupled inductor may furtherinclude first, second, third, and fourth windings wound at leastpartially around the first, second, third, and fourth rungs,respectively. The second rung may be substantially closer in thelengthwise direction to the first rung than to the third rung, and thethird rung may be substantially closer in the lengthwise direction tothe fourth rung than to the second rung. The multi-phase switching powerconverter may further include first, second, third, and fourth switchingcircuits, where each switching circuit is adapted to repeatedly switchan end of a respective one of the first, second, third, and fourthwindings between at least two different voltage levels.

(D2) The multi-phase switching power converter denoted as (D1) mayfurther include a controller adapted to control the first, second,third, and fourth switching circuits such that each of the switchingcircuits switches out of phase with respect to at least one other of theswitching circuits.

(D3) In either of the multi-phase switching power converters denoted as(D1) or (D2), the ladder magnetic core may further include a firstleakage tooth at least partially bridging a widthwise separationdistance between the two rails, where the first leakage tooth isdisposed along the length of the ladder magnetic core between the secondand third rungs.

(D4) In any of the multi-phase switching power converters denoted as(D1) through (D3): (i) the multi-phase switching power converter mayfurther include a printed circuit board, (ii) respective ends of thefirst, second, third, and fourth windings may form first, second, third,and fourth solder tabs, (iii) the first, second, third, and fourthsolder tabs may be soldered to the printed circuit board, (iv) thesecond solder tab may be substantially closer in the lengthwisedirection to the first solder tab than to the third solder tab, and (v)the third solder tab may be substantially closer in the lengthwisedirection to the fourth solder tab than to the second solder tab.

(E1) A multi-phase switching power converter may include a coupledinductor including a ladder magnetic core having a length, a width, anda height. The ladder magnetic core may include first and second railsextending in the lengthwise direction and joined in the widthwisedirection by at least first and second rungs. The coupled inductor mayfurther include first and second windings. The first winding may bewound, in a first orientation, at least partially around the first rung,and the second winding may be wound, in a second orientation, at leastpartially around the second rung, where the second orientation isopposite to the first orientation. Opposing ends of the first windingmay form first and second solder tabs, respectively, and opposing endsof the second winding may form third and fourth solder tabs,respectively. The first and third solder tabs may be disposed at leastpartially on a bottom outer surface of the first rail, and the secondand fourth solder tabs may be disposed at least partially on a bottomouter surface of the second rail. The first and second windings may bearranged such that current flowing into the first and third solder tabsflows in a common direction around each of the first and second rungs,respectively, when seen looking cross-sectionally in the widthwisedirection of the magnetic core. The multi-phase switching powerconverter may further include first and second switching circuits, wherethe first switching circuit is adapted to repeatedly switch the firstsolder tab between at least two different voltage levels, and the secondswitching circuit is adapted to repeatedly switch the third solder tabbetween at least two different voltage levels.

(E2) The multi-phase switching power converter denoted as (D1) mayfurther include a controller adapted to control the first and secondswitching circuits such that the switching circuits switch out of phasewith respect to each other.

(E3) Either of the multi-phase switching power converters denoted as(E1) or (E2) may further include a printed circuit board, and the first,second, third, and fourth solder tabs may be soldered to the printedcircuit board.

(E4) In any of the multi-phase switching power converters denoted as(E1) through (E3), each of the first and second windings may have acommon geometric shape.

(F1) A multi-phase switching power converter may include a coupledinductor including a ladder magnetic core having a length, a width, anda height. The ladder magnetic core may include two rails joined in theheightwise direction by at least first, second, and third rungsrespectively disposed along the length of the magnetic core. The coupledinductor may further include first, second, and third windings. Thefirst winding may be wound, in a first orientation, at least partiallyaround the first rung, and the second winding may be wound, in a secondorientation opposite to the first orientation, at least partially aroundthe second rung. The third winding may be wound, in the firstorientation, at least partially around the third rung. The second rungmay be substantially closer in the lengthwise direction to the firstrung than to the third rung. The multi-phase switching power convertermay further include first, second, and third switching circuits, whereeach switching circuit is adapted to repeatedly switch an end of arespective one of the first, second, and third windings between at leasttwo different voltage levels.

(F2) The multi-phase switching power converter denoted as (F1) mayfurther include a controller adapted to control the first, second, andthird switching circuits such that each of the switching circuitsswitches out of phase with respect to at least one other of theswitching circuits.

(F3) In either of the multi-phase switching power converters denoted as(F1) or (F2), the ladder magnetic core may further include a firstleakage tooth at least partially bridging a heightwise separationdistance between the two rails, where the first leakage tooth isdisposed on at least one of the two rails between the second and thirdrungs.

(F4) In any of the multi-phase switching power converters denoted as(F1) through (F3): (i) the multi-phase switching power converter mayfurther include a printed circuit board, (ii) respective ends of thefirst, second, and third windings may form first, second, and thirdsolder tabs, respectively, (iii) the first, second, and third soldertabs may be soldered to the printed circuit board, and (iv) the secondsolder tab may be substantially closer in the lengthwise direction tothe first solder tab than to the third solder tab.

(F5) In the multi-phase switching power converter denoted as (F4), thetwo rails may include first and second rails, and each of the first,second, and third solder tabs may be at least partially disposed on abottom outer surface of the first rail.

(F6) In any of the multi-phase switching power converters denoted as(F1) through (F5), each of the first, second, and third windings mayhave a common geometrical shape.

Changes may be made in the above methods and systems without departingfrom the scope hereof. Therefore, the matter contained in the abovedescription and shown in the accompanying drawings should be interpretedas illustrative and not in a limiting sense. The following claims areintended to cover generic and specific features described herein, aswell as all statements of the scope of the present method and system,which, as a matter of language, might be said to fall therebetween.

What is claimed is:
 1. A coupled inductor, comprising: a ladder magneticcore having a length, a width, and a height, the ladder magnetic coreincluding two rails extending in a lengthwise direction and joined in awidthwise direction by at least first, second, third, and fourth rungssequentially disposed along the length of the magnetic core, the laddermagnetic core further including a first leakage tooth at least partiallybridging a widthwise separation distance between the two rails, thefirst leakage tooth being disposed along the length of the laddermagnetic core between the second and third rungs; and first, second,third, and fourth windings wound at least partially around the first,second, third, and fourth rungs, respectively; the second rung beingcloser in the lengthwise direction to the first rung than to the thirdrung; the third rung being closer in the lengthwise direction to thefourth rung than to the second rung.
 2. The coupled inductor of claim 1,the first leakage tooth bridging less than all of the widthwiseseparation distance between the two rails.
 3. The coupled inductor ofclaim 1, wherein: respective ends of the first, second, third, andfourth windings form first, second, third, and fourth solder tabs,respectively, the first, second, third, and fourth solder tabs beingstructurally capable of surface mount soldering to a common substrate;the second solder tab is closer in the lengthwise direction to the firstsolder tab than to the third solder tab; and the third solder tab iscloser in the lengthwise direction to the fourth solder tab than to thesecond solder tab.
 4. The coupled inductor of claim 3, the two railscomprising first and second rails, each of the first, second, third, andfourth solder tabs being at least partially disposed on a bottom outersurface of the first rail.
 5. A coupled inductor, comprising: a laddermagnetic core having a length, a width, and a height, the laddermagnetic core including two rails extending in a lengthwise directionand joined in a widthwise direction by at least first, second, third,and fourth rungs sequentially disposed along the length of the magneticcore, the ladder magnetic core further including a first leakage toothat least partially bridging a widthwise separation distance between thetwo rails, the first leakage tooth being disposed along the length ofthe ladder magnetic core between the second and third rungs; and first,second, third, and fourth windings wound at least partially around thefirst, second, third, and fourth rungs, respectively; the second rungbeing closer in the lengthwise direction to the first rung than to thethird rung; the third rung being closer in the lengthwise direction tothe fourth rung than to the second rung; respective ends of the first,second, third, and fourth windings forming first, second, third, andfourth solder tabs, respectively, the first, second, third, and fourthsolder tabs being structurally capable of surface mount soldering to acommon substrate; the second solder tab being closer in the lengthwisedirection to the first solder tab than to the third solder tab; thethird solder tab being closer in the lengthwise direction to the fourthsolder tab than to the second solder tab; the two rails including firstand second rails, each of the first, second, third, and fourth soldertabs being at least partially disposed on a bottom outer surface of thefirst rail; and the windings arranged such that current flowing into thefirst, second, third, and fourth solder tabs flows in a common directionaround each of the first, second, third, and fourth rungs, respectively,when seen looking cross-sectionally in the widthwise direction of themagnetic core.
 6. The coupled inductor of claim 5, the ladder magneticcore further including a second leakage tooth at least partiallybridging the widthwise separation distance between the two rails, thethird and fourth rungs being disposed along the length of the laddermagnetic core between the first and second leakage teeth.
 7. The coupledinductor of claim 6, the first, second, third, and fourth windingshaving respective leakage inductance values that are identical.
 8. Acoupled inductor, comprising: a ladder magnetic core including (a) twoopposing rails extending in a lengthwise direction and (b) a pluralityof rungs divided into at least two groups of rungs, a lengthwiseseparation distance between adjacent rungs in each group of rungs beingless than a lengthwise separation distance between adjacent rungs ofdifferent groups of the at least two groups of rungs, each rung of theplurality of rungs joining the two opposing rails in a widthwisedirection of the ladder magnetic core; a respective winding wound aroundeach of the plurality of rungs; and a leakage tooth at least partiallybridging a widthwise separation distance between the two opposing rails,the leakage tooth being disposed in the lengthwise direction between twoadjacent groups of the at least two groups of rungs.